This invention relates to bisphenols and polycarbonates derived therefrom. More particularly, it relates to bisphenols of the type which may be prepared from cashew nut shell liquid.
Cashew nut shell liquid (hereinafter sometimes simply "CNSL" for brevity) has been known for years to contain compounds useful in various aspects of chemical industry, with particular reference to plastics production. It is of such interest for various purposes that technical grade distilled CNSL is a commercially available product. It comprises, in major proportion (typically about 80% by weight), a material also sold separately under the trade name CARDANOL which is a mixture of the hydroxyalkylphenols 3-(pentadec-8-enyl)phenol, 3-(pentadeca-8,11-dienyl)phenol and 3-(pentadeca-8,11,14-trienyl)phenol. Minor constituents include about 18% of a material also sold separately under the trade name CARDOL, which is a mixture of the corresponding 5-substituted resorcinols, and about 2% 2-methylcardol, which is a mixture of the corresponding 2-methyl-5-substituted resorcinols, and other materials not fully identified.
Aromatic polycarbonates are a widely used class of generally amorphous polymers characterized by such properties as transparency, durability, high impact resistance and solvent resistance. In recent years, they have been used advantageously for the fabrication of optical recording media, as exemplified by compact disks. It is very advantageous, however, to use for this purpose polycarbonates having very low birefringence values. This frequently involves the incorporation of copolymer units in a conventional polycarbonate, such as one derived from 2,2-bis(4-hydroxyphenyl)propane also known as "bisphenol A", since the birefringence values of bisphenol A homopolycarbonates are higher than is desirable.
Among the dihydroxyaromatic compounds reported to form homo- or copolycarbonates with low birefringence are 6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spiro (bis)indane ("SBI"), 2,2-bis(3-methyl4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl) cyclohexane, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and 1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene, also known as 4,4'-(m-phenylenediisopropylidene) diphenol. However, problems arise in the synthesis and use of these compounds. For example, SBI is somewhat costly to produce and affords brittle polymers, and various others of these rather exotic bisphenols are produced only at considerable expense.
It is of interest, therefore, to develop new bisphenols having the potential of affording polycarbonates with high processability and low birefringence. It is of particular interest to develop bisphenols which may be easily and cheaply obtained from readily available and renewable resource materials such as CNSL.